Dipeptidyl peptidase 1 (DPP1; EC 3.4.14.1), also known as cathepsin C, is a lysosomal cysteine protease belonging to the papain family having a molecular weight of 200 kDa. DPP1 was first discovered by Gutman and Fruton in 1948 (J Biol Chem, 174, 851-858); however, the cDNA of the human enzyme was first described in 1995 (Paris et al. 1995, FEBS Lett, 369, 326-330). DPP1 is the only member of the papain family that is functional as a tetramer, consisting of four identical subunits. Each subunit is composed of an N-terminal fragment, a heavy chain and a light chain (Dolenc et al. 1995, J Biol Chem, 270, 21626-21631).
DPP1 is constitutively expressed in many tissues with highest levels in lung, kidney, liver and spleen. DPP1 catalyses the removal of dipeptides from the N-terminal end of polypeptide substrates with broad specificity. Recent data suggest that besides being an important enzyme in lysosomal protein degradation, DPP1 also functions as a key enzyme in the activation of granule serine proteases in cytotoxic T lymphocytes and natural killer cells (granzymes A and B), mast cells (chymase and tryptase) and neutrophils (cathepsin G, neutrophil elastase and proteinase-3).
Mast cells are found in many tissues but are present in greater numbers along the epithelial linings of the body, such as the skin, respiratory tract and gastrointestinal tract. In humans, two types of mast cells have been identified. The T-type, which expresses only tryptase, and the MC-type, which expresses both tryptase and chymase. In humans, the T-type mast cells are located primarily in alveolar tissue and intestinal mucosa while the TC-type cells predominate in skin and conjunctiva. Tryptase and chymase appear to be important mediators of allergic diseases, being involved in processes of inflammation, bronchoconstriction and mucus secretion.
Neutrophils play a critical role in host defence against invading pathogens. Neutrophils are produced in the bone marrow and are fully mature when released into the circulation to take up their role as the first line of cellular defence. Pro-inflammatory mediators and chemotactic attractants activate neutrophils and draw them to the site of infection, where they act to engulf bacteria by phagocytosis, assaulting them with an arsenal of anti-bacterial compounds that use both oxidative and non-oxidative methods of attack. The powerful serine protease, neutrophil elastase, is one of those anti-bacterial compounds that are clearly involved in destroying bacteria. Neutrophil elastase is released into the phagolysome surrounding the microorganism, which it proceeds to destroy. Neutrophil elastase is able to attack the outer membrane protein, OmpA, in gram-negative bacteria, helping to directly kill the pathogen by degrading its membrane, as well as enabling other anti-bacterial compounds to gain access to the pathogen. In addition, neutrophil elastase may help process other anti-bacterial compounds, converting them from inactive pro-peptides into their active states, such as for cathelicidin.
Yet neutrophil elastase can also cause problems for its host. It is one of the most destructive enzymes in the body, with the capability of degrading extracellular matrix proteins (including collagens, proteoglycan, fibronectin, platelet receptors, complement receptor, thrombomodulin, lung surfactant and cadherins) and key plasma proteins (including coagulation and complement factors, immunoglobulin, several proteases and protease inhibitors). Under physiological conditions, endogenous protease inhibitors, such as α1-antitrypsin, tightly regulate the activity of neutrophil elastase. However, at inflammatory sites, neutrophil elastase is able to evade regulation, and once unregulated it can induce the release of pro-inflammatory cytokines, such as interleukin-6 and interleukin-8, leading to acute lung injury. It can even impair host defence against infection by degrading phagocyte surface receptors and opsonins. Its negative role is illustrated by its involvement in the tissue destruction and inflammation that characterise numerous diseases, including hereditary emphysema, chronic obstructive pulmonary disease, cystic fibrosis, adult respiratory distress syndrome, ischemic-reperfusion injury and rheumatoid arthritis.
There is strong evidence associating tryptase and chymase with a number of mast cell mediated allergic, immunological and inflammatory diseases. The fact that neutrophil elastase, cathepsin G and proteinase 3 also seem to play significant roles in these types of diseases point to DPP1 being a valid therapeutic target due to its central role in activating these proteases (Adkison et al. 2002, J Clin Invest, 109, 363-271; Pham et al. 2004, J Immunol, 173, 7277-7281).                WO2004/110988 relate to certain nitrile derivatives and their use as DPP1 inhibitors.        WO2009/074829 relate to peptidyl nitriles and their use as DPP1 inhibitors.        WO2010/128324 relate to α-amino amide nitriles and their use as DPP1 inhibitors.        WO2012/119941 relate to peptidyl nitrile compounds and their use as DPP1 inhibitors.        WO2013/041497 relate to N-[1-cyano-2-(phenyl)ethyl]-2-azabicyclo[2.2.1]heptane-3-carboxamide and their use as DPP1 inhibitors.        WO2001/096285 and WO2003/048123 relate to β-amino amide nitriles that have an inhibitory activity on cysteine proteases.        
There is no disclosure of an amide nitrile compound which bears a β-amino acid in the form of the disclosed (2S)-N-[(1S)-1-cyano-2-phenylethyl]-1,4-oxazepane-2-carboxamide compounds. We have now found that such compounds possess potent DPP1 activity and/or have desirable pharmacological activity profiles (for example a decreased risk of binding to elastin rich tissues, such as the aorta).